The present invention relates to a dishwasher wash liquid re-circulation and soil collection system, and more particularly to a system for concentrating soils in a dishwasher pump.
Typical domestic dishwashers in use today draw wash liquid from a sump at the bottom of a wash chamber and spray the wash liquid within the wash chamber to remove soils from dishes located on racks in the tub. In an attempt to improve performance and efficiency, some dishwashers employ a system for separating soil out of the recirculating wash liquid and for retaining the soils in a soil collection system. Soil collection systems frequently include a filter screen which is used to retain soil in a soil collection chamber. U.S. Pat. No. 5,165,433, for example, discloses a dishwasher system including a soil separator which sends soil laden wash liquid into a soil container whereupon the soil laden wash liquid passes through a fine filter disposed in the wall of the soil container.
In order to improve operation of soil separation systems, such as shown in the ""433 patent, it is generally desirable to attempt to concentrate soils within the recirculating wash liquid, at least to some degree, such that wash liquid having a high concentration of soils can be delivered to the soil collection system. In this manner, the soil collection system is most effectively used for removing soils from wash liquid which is recirculating through the wash chamber. Without some form of soil concentration within the recirculating wash liquid, the wash liquid sent to the soil collection system includes the average concentration of soils and, as a result, it takes a relatively long time for all of the soils to be removed from the recirculating wash liquid. Moreover, it is generally true that the longer is takes to remove soils from the recirculating wash liquid, the greater the chance that the soils may be deposited on the dishes and remain on the dishes after the wash cycle is complete.
Past dishwasher systems, such as the ""433 patent, have attempted to use centrifugal force to concentrated soils within a pump chamber. In such systems, a pump impeller is typically located within a circular pump chamber. As the impeller rotates, soils are urged to the outer periphery of the pump chamber under centrifugal force. Wash liquid from the outer periphery of the pump chamber, having a heavy concentration of soils, is then guided or directed to flow to a soil collection system. While a centrifugal concentrating system for concentrating soils, such as shown in the ""433 patent, is relatively effective in a vertical axis type pump, it is not readily adapted to a volute type pump having a spiral casing.
It is well known that volute type pumps, wherein a centrifugal pump is housed in a spiral casing so that rotational speed will be converted to pressure without shock, are highly efficient pump designs. This type of pump is used extensively in dishwashers because of its efficiency, see for example U.S. Pat. No. 4,243,431 and U.S. Pat. No. 5,268,334. In contrast, vertical axis pump systems, where the flow of wash liquid is perpendicular to the plane in which the pump impeller rotates, such as the pump system disclosed in the ""433 patent are less efficient than volute type pumps in a dishwasher.
It can be understood therefore, by one skilled in the art, that there is a need for systems to concentrate soils in recirculating wash liquid within a dishwasher. In particular, it would be an improvement to provide a soil concentration system which is readily adapted for use in a volute type pump.
The present invention, therefore, is directed to a wash liquid recirculation system for a dishwasher including a unique soil separating system. The recirculation system includes a wash pump which is provided with an internal filter plate to concentrate soils. The wash pump includes an impeller disposed within a pump housing or casing. When energized, the wash pump draws wash liquid from a sump area and pumps wash liquid through the impeller into the pump housing or casing. The filter plate is disposed within the casing for dividing the casing into a first and second region and for concentrating soils in the second region. Concentrated soils are delivered from the second region to a soil collection system. The filter plate is disposed radially outwardly from the impeller, substantially perpendicular to the rotational axis of the impeller.
According to one aspect of the present invention, the soil separating system further includes a volute pump having an impeller disposed within a spiral casing, the spiral casing having a main outlet and a secondary outlet. A filter plate is disposed within the pump housing for filtering a portion of the wash liquid pumped by the impeller through the main outlet. The filter plate is disposed radially outwardly from the impeller, substantially perpendicular to the rotational axis of the impeller. The filter plate divides the pump chamber into a first region and a second region wherein wash liquid pumped through the impeller flows into either the first region or the second region and wherein the main outlet provides an outlet for the first region and the secondary outlet provides an outlet for the second region.
According to yet another aspect of the invention, the present invention is directed to a method for separating soils from wash liquid recirculating through a wash chamber of a dishwasher. The dishwasher includes a wash pump having a pump housing and a pump impeller within the pump housing. A filter plate separates the pump housing into a first region having a main outlet and a second region having a secondary outlet. During operation of the dishwasher, wash liquid is drawn from the sump area of the wash chamber into the pump housing and pumped through the impeller into either the first or second region. Some of the wash liquid pumped into the second region is passed through the filter plate into the first region for outlet through the main outlet while another portion wash liquid, including the soils concentrated in the second region, are pumped through the secondary outlet to a soil collection system.